Recently, an in-wheel motor where a wheel is directly connected with a motor so as to drive a wheel directly has become most noticeable. However, the in-wheel motor as well as a conventional wheel driving type has one degree of freedom (DOF). Accordingly, the in-wheel motor cannot move a vehicle in all directions.
To solve such a problem, a spherical linkage or spherical wheel is applied to a wheel of the vehicle. However, a vehicle or driving apparatus using a spherical linkage or a spherical wheel (e.g., U.S. Pat. No. 4,785,899 and U.S. Patent Publication No. 2002-0153205) is hard to control or to achieve three degrees of freedom movement. Further, it is disclosed that the spherical wheel is driven by a magnetic force generated by a magnet and a coil (e.g., Korea Patent Publication No. 10-2009-0093523 and U.S. Pat. No. 6,906,441), but it is challenging to set a constant position of the magnet because the wheel of the vehicle rotates in any direction.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it can contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.